@CRSTKN, after seeing some reviews, I find it a bit hard to say if this was going to be a proper GS...
Yes, Lexus clearly loose a beautiful sedan, but it's cramped in the rear seats and it has a small boot… Considering that the GS was always a bigger car than the ES, this one seems to be worse than the current 3/3.5IS in both this areas...
It would be a beautifull but heavy, expensive and non-pratical sedan next to the competition.... Reviewers would make it sound like the worst thing Lexus ever created and most probably would be a really hard thing to sell next to a ES or even a LS... Even harder than the 4GS was with a well packaged chassis, nice to drive and spacious interior...
Given this, probably this was the best thing for Lexus since it shared some of the development cost with Toyota (turned into the Mirai) and in return get some more R&D cash to spend in the future.